Field of Invention
The invention relates generally to the field of photographic camera shutters, and particularly to electromagnetic activated camera shutters that control both the aperture size and the exposure time.
Shutters that control both the aperture and exposure time have been used to regulate the amount of light that reaches the imaging area of a filmstrip contained within a camera. Open loop systems have been utilized as taught by the prior art to control the operation of the shutter blades. In an open loop system the input to the shutter is a complex waveform that is tailored to a particular shutter, and no information about the location of the shutter blades is provided to the electronics that controls the shutter. However, the characteristics of a shutter change with time. This is due to changes in friction of the shutter's components which is caused by contamination and wear of the shutter. Thus, the same control signal will not continuously cause the camera shutter blades to form the same aperture size in the same exposure time. Thus, one of the disadvantages of the prior art is that the shutter's electronics did not know the location of the shutter blades to precisely control the size of the aperture opening and exposure time.
Another disadvantage of the prior art is that a lock in torque or reluctance torque is developed by the permanent magnet and electromagnet independent of the current in the coil of the electromagnet. This reluctance torque caused prior art electromagnet shuttering systems to be non-controllable and not capable of having many aperture openings. For instance, by incrementally varying the current in the coil of the electromagnet one would not be able to incrementally change the position of the permanent magnet so that the shutter blades will form many different aperture openings.